Exhibit 21.1 Subsidiary State of Incorporatio D/B/A Diversified NY IPA, Inc. New York None Diversified Pharmaceutical Services (Puerto Rico), Inc. Puerto Rico None Diversified Pharmaceutical Services, Inc. Minnesota None ESI Canada Holdings, Inc. New Brunswick, Canada None ESI Canada, Inc. New Brunswick, Canada None ESI Claims, Inc. Delaware None ESI Mail Pharmacy Services, Inc. Delaware None ESI Utilization Management Co. Delaware None Express Scripts Sales Development Co. Delaware None Express Scripts Specialty Distribution Services, Inc. Delaware None Express Scripts Vision Corporation Delaware ESI Vision Care IVTx, Inc. Delaware Express Scripts Infusion Services Great Plains Reinsurance Company Arizona None Practice Patterns Science, Inc. Delaware None Value Health, Inc. Delaware None ValueRx of Michigan, Inc. Michigan None YourPharmacy.com, Inc. Delaware None 607486 Alberta Ltd. Albert, Canada None